It has long been the practice to drive the agitator in the nozzle of an upright vacuum cleaner by the fan motor through a simple friction belt drive, but in such cleaners the dirt-laden air from the nozzle passed through the fan before entering the dust bag and the type of fan capable of handling dirty air required a large heavy impeller driven at a slow speed. The impeller, which was mounted directly on the motor shaft, had greater inertia than the agitator and hence acted to limit the rate of acceleration and if it were a little too great, the friction belt could slip without undue damage. Likewise if the agitator were stalled, the belt could slip and thus prevent motor stalling and consequent overheating of the motor. A belt and drive system of this type could also slip under normal operating conditions and thus reduce the speed of the agitator and introduce possible belt wear.
On the other hand, in cleaners in which the dirty air is first passed through the dust bag so that only clean air passes through the fan, a small, lightweight impeller driven at high speed, in the neighborhood of 20,000 rpm and producing a high suction, may be employed. In such cleaners, however, it has been the practice to provide a separate small lower-speed motor for driving the agitator through a positive drive, such as a toothed timing belt, and protecting the motor from damage resulting from a stalled agitator by means of an overload circuit breaker, as is shown in U.S. Pat. No. 3,266,078 issued Aug. 16, 1966.